The present invention relates generally to one-time programmable non-volatile memory elements and more specifically to an encoding scheme to reduce sense current in a poly fuse array.
Fuses are usually one-time programmable (OTP) devices. In other words, fuses cannot be reprogrammed once they are programmed. Poly fuses, also a type of OTP non-volatile memory (NVM), are used in programmable devices as integrated circuits increasingly require embedded NVM. Fuse memory can be programmed to configure an integrated circuit, to store die information, program instructions, configuration information and other relevant information.
Data is stored based on the condition of the fuse. A fuse may have a low resistance state or a high resistance state. A programmed fuse may be blown to indicate a high resistance state. And similarly, a blown fuse may represent a logic one value while an unblown fuse may represent a logic zero value. Hence, the different states represent specific logical states at any one time in an array of fuses. Sensing circuits are used to sense the state of the fuses. Poly fuses have different sense currents depending on the state of the fuse at any one time. An unblown fuse, for instance, may require more sense current compared to a blown fuse. Therefore, the sense current is highly dependent on the number of blown and unblown fuses.
It is highly desirable to have a method that will reduce the fuse sensing current, thereby reducing the overall power bussing requirement in a poly fuse array. It is also advantageous to have a power-saving scheme that does not substantially increase die area of the array.